Following another excellent discussion on Primary and Secondary‘s Workbench group on Facebook, I’ve come up with a list of what separates the wheat from the chaff when it comes to a gun that’s ‘duty grade’ as opposed to being a ‘hobby plinker’.
There are basically two classes of AR-15s. The ones you use for killing soda cans and the ones you use for saving your life. There are individual rifles in the budget category that are surprisingly reliable– some people have had 10,000 rounds through their budget PSA or DPMS lower, or even a Carbon-15, with no trouble. However, a statistically significant number of folks have run into serious, even catastrophic failures of their weapons during training events. Carbon-15s are notorious for the top rail walking off; DPMS has issues with their various small parts in the bolt and LPK. You don’t need a Grizzly LAR or a 3,000 dollar full custom AR-15. Some research and a good eye for detail will help you find out which parts are the real deal.
If you’re going to trust an AR-15 to save your life, you need to do the work to make sure the material metal isn’t cheap steel from China and the parts aren’t being made by the lowest bidder– or worse, an importer. There are some flaky people out there who’ll happily sell you a part ‘made in the USA’ that was actually manufactured in China or Taiwan.
1: Buffer Tube. A cheap buffer tube will fold or collapse under stress. Regular shooting probably won’t break one, but mortaring the weapon to clear a stoppage or falling on it can bend the tube. A 5-degree bend in the stock will cause a catastrophic failure.
2: Crane Stock: A cheap traditional crane stock has a lot of slop in it, affecting accuracy. If the cam pin wears down, the stock will collapse under recoil. Repeatedly mortaring the weapon to clear stoppages can exacerbate this.
3: Lower Receiver: Cast or polymer lowers have a slightly higher risk of flaws at key locations. A /really/ cheap receiver that isn’t made from quality T6 aluminum can strip out at the buffer tube threads, or the takedown pins can wear and walk out. Trigger pins might even not be drilled in the proper locations, creating more wear on those parts and potentially not aligning the hammer with the firing pin.
4: LPK Springs: Cheap springs are unreliable. If they’re simple steel, they’re more prone to rusting and inconsistent quality in the metal can cause abrupt failure or loss of strength due to heat.
5: Barrel Nut: If improperly installed, too much torque can cause stripping and damage to the upper, significantly shifting POI and potentially causing the upper to crack prematurely. If too loose, the barrel will walk around and have severely degraded accuracy as well as hugely accelerated wear.
6: Bolt Carrier Group: Cheap, cast-metal extractors can snap. If the bolt is very out of spec, it can lead to issues locking up properly into the chamber or create an dangerous headspace situation, increasing wear. Cheap firing pins and retaining pins are known to crack and fail as well. A rough texture finish on the BCG components can also increase the accumulation and effect of fouling– if you can see visible machine marks, it is not a quality product.
7: Gas Block: If your gas block is not properly aligned with the gas port, you’ll have issues with low bolt velocity. A clumsily installed gas tube can end up crimped or bent, with similar effect. Failing to dimple or properly pin the gas block in place can lead to it being knocked out of alignment during aggressive manipulation and in budget guns, failing to align it properly is a common cause of cycling issues.
8. Bolt Carrier Key: The gas key on the carrier must be staked. If it is not, then it can come apart under normal operation and completely deadline the weapon.
9. Castle Nut: The castle nut, if not staked, can come unscrewed after a few thousand rounds. If it does, your retaining plate will slip out; this will let your takedown detent spring pop loose and potentially cause your rear takedown bolt to fall out.
10. Charging Handle: The classic mil-spec charging handle has a single 1/16th roll pin holding the latch in place. One-handed manipulation can break that latch off. An upgraded, heavy charging handle is recommended.
If you’re going for sub-MOA precision at 100 yards or trying to get your split times as low as possible there are all kinds of cool bells and whistles and toys to add. But these represents the 10 most common failures of the AR-15, and the ones that are easiest to fix if you’re trying to turn your ‘starting gun’ into something for more serious use.
threegunguys 
